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The Ultimate Reloading Manual
Wolfe Publishing Group
  • reloading manual
  • alliant reloading data
  • reloading brass
  • shotshell reloading
  • bullet reloading
The Ultimate Reloading Manual
load development

Subcaliber Adapters

Author: Bob Campbell / Wolfe Publishing Co.
Date: Nov 28 2012

Adapters in .22 Short and .22 Magnum for the
.223, the .32 ACP adapter and the .30 Carbine
adapter. These adapters were in a storage
room for over five years and picked up
a little surface rust, but they clean
up well! These well-made units
are from Alex, Inc.

While it may require some imagination to find practical application for subcaliber adapters, they do not represent a significant investment, and the results are interesting. Introducing young shooters to centerfire shooting is one chore they can handle, small game hunting with a big game rifle is another.

The subcaliber chamber insert consists of an adapter with two parts. The adapter itself is well machined of good material with excellent finish. The adapter resembles a cartridge case and is specific to the caliber. In other words, you need a .30-06 adapter for the .30-06 and a .308 for the .308. The base of the adapter is a firing device. It is removed to insert a subcaliber round, such as the .32 ACP or .32 Smith & Wesson Long, and each adapter is also specific to the subcaliber cartridge specified. The base contains an inertia firing pin that is struck by the rifle’s firing pin. When the subcaliber cartridge is inserted, the base is pressed into place, and the insert is loaded in the same manner as any other cartridge. An extraction groove is milled into the bottom of the adapter in the same place as with a standard cartridge to facilitate extraction. Once the cartridge in the adapter is fired, the adapter is extracted in the normal manner. A bullet nose serves to press the spent case into the adapter just a bit. This budges the base of the adapter enough to grasp and remove the base from the adapter. I simply shake the spent cartridge from the adapter. Then we start over.

This is how the adapter works – remove the base, insert the cartridge, replace the base.

This is not a high-speed device, but the adapters are inexpensive enough that you may keep several on hand if your desire is to fire a string instead of a single shot. Due to the construction of the units, they normally have a good tight fit to the chamber and offer good accuracy. The pistol cartridge conversions use cartridges that do not have enough sectional density for accuracy or effect at 100 yards, but to 50 yards they are great devices for marksmanship practice and even small game hunting. The .32 ACP, as an example, is very accurate when fired in the long barrel of a .30-06 rifle. The Speer Gold Dot or the Federal Hydra Shock hollowpoint bullets expand well and are deadly on small game. The .32 Smith & Wesson Long insert is my favorite of the two .32s, and this one is particularly well suited to use with cast bullet handloads, especially the Magnus 100-grain semi-wadcutter (SWC). I have also enjoyed good results with handloads using the Hornady 60-grain XTP in both calibers.

This bullet is light enough that some expansion is realized in the pistol calibers. The long barrel of a rifle provides good velocity but, surprisingly, very little velocity, if any, over a 4-inch pistol barrel.

Let’s talk about velocity. I had quite a surprise with the .32 ACP insert. As a rule, with the standard loads in .32 ACP, velocity is less with the rifle than with a pistol. It is simply true. The reason must be that the cartridge isn’t very powerful and the bullet simply drags going through the barrel. As an example, the zippy Fiocchi 71-grain FMJ bullet exits the Walther PP at about 1,005 fps. From the Enfield .30-06, 775 fps was realized. A few loads using the slower powder choices meet or beat pistol velocity. With the .32 Smith & Wesson Long and the various slower-burning powders we saw a modest increase in some loads but never more than 25 fps over the pistol calibers. Again, a bit surprising compared to our experience with the .22 Long Rifle and .357 Magnum, but considering the modest powder charges used, we should not have been surprised. Power isn’t increased but accuracy is.

While the pistol calibers are the most economical, I also own a subcaliber insert in .30 Carbine that offers much greater velocity than the pistol cartridge adapters and makes for a reasonable alternative for use at longer range. The .30-caliber carbine is a fine pest popper, but when used in a quality bolt-action rifle, it is far more accurate than we would have believed. Just the same, most of my experience revolves around the .32 ACP adapter. I recently enjoyed an outing with my young daughter and an Enfield .30-06 rifle. This rifle is in excellent condition, although the stock was replaced with commercial wood at some point in the past. Since the collector value was gone, I had set the rifle aside in hopes that one day I would run across an affordable original military issue stock set. A better solution was realized.

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